I used to go to playgroups when I lived in a very small town that had no other options outside of individual playdates.
I never thought of it the way you've said it, but I would agree with you from my experience.
Once I moved to a city (kids were 2 1/2 and 4) I stopped going and instead started doing more things with the kids with friends. I found the dynamics of my friends changed because we didn't stand around comparing ourselves and trying to prove we were better at being a `mom' than the other moms.
Women have to start supporting eachother instead of ripping eachother down. There's a lot of ripping down in the playgroups I've gone to (myself included - you kinda get sucked into that behaviour)